1. Field of the Invention
This invention relates to a system for controlling fuel metering in an internal combustion engine, more particularly to a system for controlling fuel metering in an internal combustion engine wherein the actual cylinder fuel flow is constantly maintained at a desired value by adaptively compensating for the fuel transport delay caused by adherence of the injected fuel to the wall of the intake manifold and the like. Also, this invention relates to a method for estimating cylinder air flow inducted in a cylinder of the engine.
2. Description of the Prior Art
During transient engine operation, a cylinder fuel flow is apt to be out of a desired value, and a lean or rich spike occurs in the air/fuel ratio. One cause for this is fuel transport delay caused by the adherence of fuel to the wall of the intake manifold etc. The behavior of the fuel transport delay changes depending on the operating states of the engine, initial manufacturing variance, and time-course changes of the intake manifold or the like owing to the adherence of deposits its wall. With a view to overcoming the problems caused by fuel transport delay, Japanese Laid-open Patent Publication Nos. 2(1990)-173,334 and 3(1991)-26,839 propose that fuel metering in an internal combustion engine be controlled by incorporating adaptive control in which a fuel adherence plant and a parameter adjuster are established such that the plant's output, i.e., an actual cylinder fuel flow coincides with a desired value even during transient operating state of the engine.
For adaptively compensating for fuel transport delay in a multicylinder internal combustion engine, however, it is indispensable to determine the air/fuel ratio at the individual cylinders with high precision so as to be able to estimate accurately the actual cylinder fuel flow inducted into the individual cylinders. Since the prior art controls proposed in the aforementioned references immediately use the air/fuel ratio measured at the exhaust gas confluence point for the whole cylinders, however, it is not able to estimate the actual cylinder fuel flow inducted into the individual cylinders with good accuracy.